Downhole testing of a hydrocarbon containing formation of interest is often performed to determine whether commercial exploitation of the formation is viable and how to optimize production from the formation. For example, after a well or well interval has been drilled, zones of interest are often tested to determine various formation properties such as permeability, fluid type, fluid quality, formation temperature, formation pressure, bubblepoint, formation pressure gradient, mobility, filtrate viscosity, spherical mobility, coupled compressibility porosity, skin damage (which is an indication of how the mud filtrate has changed the permeability near the wellbore), and anisotropy (which is the ratio of the vertical and horizontal permeabilities).
To perform formation testing, a formation testing tool is typically lowered downhole on a wireline or tubing string (e.g., a drill string). A region of the formation of interest is isolated from wellbore fluids, and valves or ports of the tool are opened to allow formation fluids to flow from the formation into a sampling chamber of the tool while pressure recorders measure and record the fluid pressure transients. The sample chamber of the formation testing tool may be formed by a cylinder. The volume of the sample chamber may be increased or decreased by translating a piston within the cylinder. To initiate fluid flow from the formation into the sample chamber, the piston is translated in the cylinder to increase the volume of the sample chamber, thereby lowering the fluid pressure inside the sample chamber in a process referred to as “drawdown.” After drawdown is completed, formation fluid continues to flow into the sample chamber in a process referred to as “buildup.” Conventionally, the pressure of fluid inside the sample chamber is monitored and recorded until it stabilizes, which indicates the formation pressure has been reached. The length of time required for the pressure to stabilize is referred to as the “stabilization” time, and conventional single drawdown/buildup tests for low mobility reservoirs may require several hours or days to stabilize, causing the loss of valuable drilling rig time.
To reduce formation testing time, pressure pulsing formation testing methods have been developed. According to such testing methods, (1) drawdown is performed as described above, (2) buildup is performed for a finite period of time less than the stabilization time, (3) the volume of the sample chamber is then decreased to generate a pressure pulse and inject a small amount of fluid back into the formation in a process referred to as “injection” or “pressure pulsing”, and (4) fluid in the sample chamber is allowed to continue to flow into the formation in a process referred to as “builddown” until the pressure stabilizes, which indicates the formation pressure has been reached. A formation pulse test sequence may include a single pulse test or a sequence of multiple pulse tests.